Sanitize summary field in search results

Why are these changes being introduced:

* Some summaries had HTML tags that were being rendered as text in
  the search results. Sanitizing the summary field allows certain
  HTML tags to be rendered properly while stripping out potentially
  harmful tags.

Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/USE-297

How does this address that need:

* Uses rails `sanitize` helper to allow certain HTML tags in the
  summary field while stripping out others.

Document any side effects to this change:

* I'm using sanitize with no parameters which seems to look good.
  If we find we want slightly different behavior we can dig deeper into
  what tags/attributes to allow.

Author: JPrevost

app/views/search/_result.html.erb

@@ -47,7 +47,7 @@
 
       <% if result[:summary].present? %>
         <div class="result-summary truncate-list">
-          <span class="sr">Summary: </span><%= result[:summary] %>
+          <span class="sr">Summary: </span><%= sanitize result[:summary] %>
         </div>
       <% end %>
     </div>

app/views/search/_result_primo.html.erb

@@ -54,7 +54,7 @@
 
       <% if result[:summary].present? %>
         <div class="result-summary truncate-list">
-          <span class="sr">Summary: </span><%= result[:summary] %>
+          <span class="sr">Summary: </span><%= sanitize result[:summary] %>
         </div>
       <% end %>
     </div>